Sub-millimeter and infrared reflectarray

ABSTRACT

An integrated sub-millimeter and infrared reflectarray includes a reflective surface, a dielectric layer disposed on the reflective surface, and a subwavelength element array and a subwavelength element array electromagnetically coupled to the reflective surface. The subwavelength element array includes (i) electrically conductive subwavelength elements on the dielectric layer, (ii) wherein the dielectric layer comprises a plurality of dielectric subwavelength elements, or (iii) the dielectric layer includes a plurality of embedded dielectric subwavelength elements. The array includes at least one of a plurality of substantially different inter-element spacings and a plurality of substantially different dimensions for the elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/749,248 entitled “SUB-MILLIMETER AND INFRARED REFLECTARRAY”, filed onDec. 9, 2005, the entirety of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The invention relates to reflector antenna technology, more specificallyto integrated reflectarrays.

BACKGROUND

A conventional reflector antenna is parabolically shaped to providefocusing of plane waves. A “Flat Parabolic Surface” (FLAPS™) is a devicecurrently marketed by Malibu Research, Camarillo Calif. FLAPS™ is anantenna design which utilizes a geometrically flat surface havingsurface features which behaves electromagnetically for incident RFradiation as though it were a parabolic reflector.

The FLAPS™ generally consists of an array of dipole scatterers. Theelemental dipole scatterer consists of a dipole positioned approximately⅛ wavelength above a ground plane on top of a dielectric layer. IncidentRF energy causes a standing wave to be set up between the dipole and theground-plane. The dipole itself possesses an RF reactance which is afunction of its length and thickness. This combination of standing-waveand dipole reactance causes the incident RF to be reradiated with aspecific phase shift, which can be controlled by a variation of thelength of the dipole. The exact value of the this phase shift is afunction of the dipole length, thickness, its distance from theground-plane, the dielectric constant of the intervening layer, and theangle of the incident RF energy. When elements are used in an array, theelements are affected by nearby elements.

The elemental scatterer performs the function of a radiating element anda phase shifter in a space fed phased array. Since dipoles of differentlengths will produce a phase shift in the incident wave, arranging thedistribution and the lengths of the dipoles can be used to serve tosteer, focus or shape the reflected wave. An array of such elements canbe designed to reradiate with a progressive series of phase shifts sothat an RF beam is formed in a specific direction. Conventionalreflector antenna calculations apply to determine surface tolerances,gain, sidelobes, and other electrical antenna parameters.

Although FLAPS™ provides effective signal processing for incident RFenergy, the minimum obtainable geometries being mm-scale for formingFLAPS™ surfaces based on a process comprising etching from double-layerprinted-circuit boards generally limits signal processing to RFwavelengths up to only about 100 GHz. Reflectarrays that process higherfrequency bands (greater than 300 GHz), such as sub-millimeter, infraredand visible, would be desirable to replace more expensive and sometimesunreliable conventional polished or diffractive optics and quasi-optics.However, besides strong challenges in obtaining required feature sizesto process shorter wavelength radiation, such a device would need toovercome challenges including modeling complexities and lack of suitablemodeling software, increased attenuation loss in metals, and frequencydependent dielectric properties.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments which are presentlypreferred, it being understood, however, that the invention can beembodied in other forms without departing from the spirit or essentialattributes thereof.

FIG. 1( a) shows a highly simplified portion of a conductivereflectarray (CR) according to an embodiment of the invention comprisingan array of electrically conductive elements disposed on a dielectriclayer. Although only four (4) elements are shown, practical CRsgenerally comprises millions or billions of individual conductiveelements.

FIG. 1( b) shows a highly simplified portion of a dielectricreflectarray (DR) according to an embodiment of the invention comprisingan array of dielectric elements disposed on a reflective surface/groundplane. Although only four (4) elements are shown, practical DRsgenerally comprises millions or billions of individual dielectricelements.

FIG. 1( c) shows a highly simplified portion of a dielectricreflectarray (DR) according to an embodiment of the invention comprisinga dielectric layer comprising a plurality of embedded dielectricelements. Although not shown, practical DRs based on embedded elementsgenerally comprises millions or billions of individual dielectricelements.

FIG. 2( a) shows array modeling results for the near-field reflectedphase as a function of patch size (square patch; in μm) for a singlecell, wherein the patches are on a BCB dielectric above a gold groundplane.

FIG. 2( b) shows a simplified model depiction a reflectarray accordingto the invention designed to planarize an infrared spherical wave front.

FIG. 3( a) is a depiction of an initial design layout of a reflectarrayproof of concept wafer based on electrically conductive microscaleelements to form an electrically conductive reflectarray (CR). Three (3)stripes are shown, with patch details for one of the three (3) stripesalso provided.

FIG. 3( b) is a scanned image showing three (3) rows of elements, therows being equally spaced, with each row having different sizeelectrically conductive elements.

FIG. 4 shows a scanned image of a CR proof of concept wafer showingwhich has sufficient resolution to show the individual array elementswithin a stripe.

FIG. 5 shows a scanned interferogram of a reference wafer illustratingno significant reflected phase aberrations.

FIGS. 6-7 shows scanned interferogram images of a CR proof of conceptwith a variable number of fringes across the wafer illustratingcontrolled phase manipulation.

SUMMARY

An integrated sub-millimeter and infrared reflectarray includes areflective surface, a dielectric layer disposed on the reflectivesurface, and a subwavelength element array electromagnetically coupledto the reflective surface, the subwavelength element array comprising:

(i) electrically conductive subwavelength elements on said dielectriclayer,

(ii) wherein said dielectric layer comprises a plurality of dielectricsubwavelength elements, or

(iii) said dielectric layer includes a plurality of embedded dielectricsubwavelength elements,

The element array includes at least one of a plurality of substantiallydifferent microscale inter-element spacings and a plurality ofsubstantially different microscale dimensions for the elements.

As used herein, “subwavelength” refers to element dimensions orinter-element spacings that are less than the wavelength of theradiation being processed by the reflectarray. “Microscale” as usedherein refers to dimensions less than 1 mm, typically being 1 to 10 μm.

Regarding the embedded dielectric feature embodiment, the embeddeddielectric subwavelength elements can comprise voids in the dielectriclayer. In this embodiment, the embedded dielectric subwavelengthelements preferably comprise a dielectric material having a dielectricconstant lower than a high dielectric constant material comprising thedielectric layer.

Regarding the embodiment where the dielectric layer comprises aplurality of dielectric subwavelength elements, the dielectric layer cancomprise Si or Ge. A planar substrate support can be interposed betweenthe dielectric layer and the reflective surface.

The microscale elements can have length and width dimensions both from 1to 10 microns. In one embodiment, the thickness of the dielectric layeris from 200 to 600 nm. The dielectric layer can comprise ZrO₂ or BCB. Anoperating frequency band of said the reflectarray can be in a rangebetween 1 THz and 500 THz.

DETAILED DESCRIPTION

An integrated sub-millimeter and infrared reflectarray includes areflective surface, a dielectric layer disposed on the reflectivesurface, and a subwavelength element array and a subwavelength elementarray electromagnetically coupled to the reflective surface, thesubwavelength element array comprising (i) electrically conductivesubwavelength elements on the dielectric layer, (ii) wherein thedielectric layer comprises a plurality of dielectric subwavelengthelements, or (iii) the dielectric layer includes a plurality of embeddeddielectric subwavelength elements. The element array includes at leastone of a plurality of substantially different microscale inter-elementspacings and a plurality of substantially different microscaledimensions for the elements.

As used herein, “substantially different” as applied to inter-featurespacing and element dimensions refers to a range of at least 0.5%. Inthe case of element dimensions, only one of the thickness, length andwidth need be substantially different. An array having differentinter-feature spacing and element dimensions is also within the scope ofthe present invention. The reflectarray may also include a substratesupport, such as silica, which can be planar or non-planar.

As defined herein, a “reflectarray” is a passive structure, made up ofan element array comprising hundreds of thousands, millions, or billionsof discrete elements. The elements can be electrically conductive ordielectric elements with each element in the array having specificreflectivity characteristics that in combination provides reflectedphase front manipulation. When the reflectarray design is based onelectrically conductive microscale elements, the reflectarray isreferred to herein as a conductive reflectarray (CR). Electricallyconductive elements include metal, highly doped semiconductors, as wellas polymeric conductors. When the reflectarray design is based ondielectric microscale elements, the dielectric elements are eitheretched into the dielectric layer, or the dielectric layer comprises anarray of dielectric microscale elements disposed on the reflectivesurface, the reflectarray being referred to herein as a dielectricreflectarray (DR).

In the case of the DR embodiment having the dielectric elements on thereflective surface, the dielectric is generally deposited onto thereflective surface of the reflectarray in the desired geometrical shapesusing a standard e-beam development process. In the case of the DRembodiment having the elements etched into the dielectric layer, thedielectric material is generally uniformly deposited across thereflective surface of the reflectarray to form a thin film. An etch orother removal process is preferably used to selectively removedielectric regions to form a pattern of voids, leaving behind thedesired geometric pattern in dielectric. Optionally, the voids can befilled with a dielectric material different from the dielectric materialcomprising the dielectric layer, generally providing a lower dielectricconstant.

As defined herein the term “reflective surface” refers to a surfacewhich provides enough reflectivity for adequate reflectarray operationin a desired operating band. Adequate reflectivity is generally at least50%, and is preferably at least 70%, and most preferably at least 90%.Generally, the reflective surface will comprise a ground plane.

However, reflective surfaces according to the invention can comprisereflective structures other than ground planes, such as distributiveBragg reflectors (DBR) and photonic band gap structures. For example,U.S. Pat. No. 6,035,089 to Grann et al. discloses photonic band gapstructure comprising a resonant grating structure in a waveguide andmethods of tuning the performance of the grating structure. Moreover,the reflective surface can comprise a frequency selective surface (FSS).

As defined herein the term “sub-millimeter and infrared” refers towavelengths less than about 1 millimeter, or equivalently, frequenciesgreater than about 300 GHz. In one embodiment, the operating frequencyis in the THz range, such as 1 to 500 THz.

FIG. 1( a) shows a highly simplified portion of a conductivereflectarray (CR) 100 according to an embodiment of the invention. CR100 includes an array of electrically conductive elements 105 disposedon a dielectric layer 110. Although four (4) elements 105 are shown, CR100 generally comprises millions or billions of individual electricallyconductive elements. Supporting substrate 102, such as a silicasubstrate, is shown. Ground plane 104 such as a Au layer, is beneathdielectric layer 110.

FIG. 1( b) shows a highly simplified portion of a dielectricreflectarray (DR) 120 according to an embodiment of the invention. DR120 includes an array of dielectric elements 125 on a reflectivesurface/ground plane 130. As with CR 100, although only four (4)elements 125 are shown, DR 120 generally comprise millions or billionsof individual elements. A substrate 122 shown in FIG. 1( b) is alsogenerally provided for mechanical support.

FIG. 1( c) shows an simplified portion of a dielectric reflectarray (DR)150 according to an embodiment of the invention based on the dielectriclayer comprising a plurality of embedded dielectric elements 161 withina dielectric layer 165. Dielectric layer 165 is disposed on a reflectivesurface/ground plane 170. A substrate 175 shown in FIG. 1( c) is alsogenerally provided for mechanical support. Embedded dielectric elements161 shown are periodic and four (4) elements in total are shown. As withCR 100 and DR 120, although only four (4) embedded dielectric elements161 are shown, DR 150 generally comprises millions or billions ofindividual embedded dielectric elements. The material comprisingembedded dielectric elements 161 preferably provides a dielectricconstant that is significantly lower as compared to the higherdielectric constant material comprising dielectric layer 165. In oneembodiment the embedded dielectric elements 161 can comprises-voidswhich are generally filled with air. Embedded dielectric elements 161can be a portion of or the full thickness of dielectric layer 165. Sucha structure can behave based on the same principle as the DR 150 shownFIG. 1( b), and is particularly useful if a second layer is desired tobe developed on top of a DR, or if the dielectric elements in the DRrequire structural support.

The reflectarray is generally an integrated reflectarray. As definedherein the term “integrated” refers to one piece structural memberformed using conventional integrated circuit processing, such as usingdepositions, lithography and etching. Integrated devices may becontrasted with devices having two or more separate components, asprovided by conventional polished optics or diffractive optics baseddevices. Integrated circuit processing leads to low cost since a givenwafer generally provides hundreds or thousands of die, and the abilityto form electronic, optical and/or MEMS devices on the same die.

Although not seeking to be bound by the mode of operation, nor necessaryto practice the CR embodiment of the present invention, the Inventorsprovide the following regarding the mode of operation. The desiredreflected phase front modification from incident radiation is achievedby the electrically conductive microscale elements, which electronicallyintroduces desired degrees of phase shift to the incident radiation ateach small unit cell of the structure. It is the interaction between theelectrically conductive microscale elements, the dielectric layer, andthe reflective surface, in the presence of an incident radiation, whichcauses the incident radiation to be reflected by each unit cell with aspecific phase shift to introduce constructive and destructiveinterference to form a desired reflected phase front.

It is believed that the far-field reflected phase for CR reflectarraysaccording to the invention can be controlled almost entirely by thedimensions of the array elements if all other dimensions of the designare held constant. As a general rule of thumb, the nominal elementdimensions are about 50% of the wavelength of the radiation to beprocessed when using a low loss, low permittivity dielectric andhalf-wave element spacing. Exemplary elements include a patch, a stubtuned patch, and a crossed dipole. Examples of other various knownelectromagnetically-loading elements which may be used with the presentinvention can be found in U.S. Pat. Nos. 4,656,487; 4,126,866;4,125,841; 4,017,865; 3,975,738; and 3,924,239. In a preferredembodiment, an array of variable size patches is used.

Variable size patches are generally preferred because they supportpolarization selectivity, are generally easier to fabricate, faster tomodel, and do not require stacking to achieve desired reflectarraybehavior. Moreover, at least for RF applications, it is known that thevariable size patch reflectarrays have wider operating bandwidths thanother common element layouts.

Conductive reflectarrays are generally formed by varying the dimensionsof a patch (or other element) on top of a ground plane backed shortdielectric layer. There exists a band (range) of patch sizes where thereflection coefficient will go through approximately 360° of phaseshift. Re-radiation inside this operating band occurs both due to theground plane and the patch. Re-radiation outside this band occurslargely due to a single dominant element (ground plane or patch).

The dielectric layer for the CR should generally be very thin relativeto wavelength of the radiation and provide a low permittivity and loss.ZrO₂ is a preferred dielectric since it provides both low loss and lowpermittivity from 1-11 μm. Bis-benzocyclobutene (BCB) is also apreferred dielectric due to its low loss and low permittivity in theinfrared band and its ability to be deposited by a spin coating process.The height of the dielectric will generally determine thephase-transition range. The permittivity of the dielectric willgenerally determine the optimum median patch size.

Although not seeking to be bound by the mode of operation, nor necessaryto practice the DR embodiment of the present invention, the Inventorsprovide the following regarding mode of operation. If a thin film isdeposited on top of a perfectly reflecting surface, the phase andmagnitude of a monochromatic wave reflected off this two materialsurface will be almost entirely dependent on the thickness andpermittivity of the film and the orientation of the incident electricfield. If the dielectric film is replaced with a periodic,sub-wavelength array of composite materials containing two dielectrics,the effective index, or permittivity, that the incident wave willobserve will be determined by the index of the two composite materialsand their periodic size ratio (the more of one material provided themore effect it will have on the effective index of the composite thinfilm).

For the DR, phase control is generally achieved by varying the periodicsize ratio across the device with a fixed periodicity and thickness tovary effective permittivity only, just as the size of the conductiveelements is varied in the CR design as described above. For the DRdesign, it is generally preferable to use the largest range ofpermittivities possible. Accordingly, the void can be filled with air(permittivity of 1) and the dielectric comprise a high permittivity, lowloss dielectric, such as Silicon (Si; Si real part of permittivity isabout 11.5) or Germanium (Ge; Ge real part of permittivity is about 16).

Unlike many traditional scattering devices such as frequency selectivesurfaces (FSS) which generally use a single element replicated aplurality of times, no practical design equations or reasonableanalytical approaches exist for reflectarrays according to the inventionwhen multiple element sizes, or element spacings, are used in the array.To overcome this challenge, numerical electromagnetic solvers have beenutilized for the invention to predict reflectarray behavior of singleelements making up the reflectarray device. One method of modelingreflectarrays according to the invention uses HFSS™ (a numerical solver)provided by Ansoft Corp. HFSS™ (Ansoft Corporation Pittsburgh, Pa.) iswidely used for the design of on-chip embedded passives, PCBinterconnects, antennas, RF/microwave components, and high-frequency ICpackages. Modeling of the aggregate device can be approximately modeledusing a ray-tracing solver, such as Optical Research Associates Code V™(Pasadena, Calif.).

Before fabrication of a new design, element (e.g. patch) dimensions aredetermined for the reflectarray to provide the desired operation, suchas focusing for IR radiation, for example. Numerical modeling takes intoaccount system non-idealities, such as lossy materials or surfacecoupling, which are difficult to incorporate into the simple analyticalapproaches without a significant increase in complexity. In HFSS™, thebehavior of individual element dimensions can be determined bydeveloping an appropriate representative model of the element andbounding the single element with periodic boundaries to approximate aninfinite array. The periodic boundaries generally lead to someinaccuracy because the actual reflectarray elements will not be in aninfinite array and the element may be placed next to elements withdifferent dimensions. This error generally can only be accounted forthrough measurement. Excitation of the model is either a plane wave or awave port, with appropriate polarization and angle of incidencereflective of the actual excitation of the desired reflectarray.Determination of the phase and magnitude response of the reflectarrayelement can be found from the scattering matrix calculated at the waveport or the phase of the calculated far-field electric field.

In most cases, it is not desirable to determine the phase response of anelement with only a single fixed dimension. Thus, several variouselement dimensions are generally characterized while fixing all otherdimensions (thickness, materials, etc.). FIG. 2( a) displays a simulatedtypical phase response of CR patch square elements for 10.6 μm radiationas a function of varying the width and length equally for elementswithin a fixed until cell size. The unit cell was 5.5 μm by 5.54 μm,where the patch is within the unit cell. In general, the zero degreephase shift value is selected to be near ½ of the wavelength of theradiation in the media of the reflectarray. It can be seen that a phaseshift from +180 degrees to −120 degrees is provided for 10.6 μmwavelength (free space) radiation by changing the patch dimension of thesquare patch from 2.4 to 4.5 μm.

With knowledge of the phase response associated with each dimensionvariation, and the wavelength band to be processed, it is possible tobegin constructing the aggregate reflectarray device. It is assumed theincident phase front will be known in advance and, thus, it should bepossible to determine the desired phase response discretely across thereflectarray for an arbitrary reflected phase front, as described above.

For example, FIG. 2( b) shows a simplified model depiction areflectarray according to the invention designed to planarize anincident spherical wave front. The incident phase front to be planarizedhas the spherical phase as a function of relative distance depicted inFIG. 2( b). A reflectarray according to the invention having the phaseresponse as a function of relative distance shown using dashed lines inFIG. 2( b) is provided. Such a response can be realized by providing aminimum patch size in the center of the array and aligning the wavefront to the center of the array, wherein domains of increasing patchsize are provided to provide an decrease in phase shift as shown in FIG.2( a) to closely match the phase as a function of distance shapedepicted in FIG. 2( b) for the incident phase front to be planarized. Asa result, the resulting reflected phase front as shown becomes planar asdesired. As those having ordinary skill in the art will recognize,reflectarrays according to the invention can process a variety ofincident phase front shapes, and provide a variety of reflected phasefront responses.

For more advanced applications, where phase front is significantlycomplicated, it may be desirable to approximate the reflectarray as anideal surface or thin film and model its response using a ray tracingpackage, such as Code V™. With Code V™, the response of the reflectarraycan be refined and more advanced analysis, such as aberrationcorrection, can be explored.

It is noted that neither modeling approach, HFSS™ or Code V™, can fullycharacterize the response of the entire array electromagnetically. Giventhe large number of elements present in the proposed invention, theamount of time and computing resources necessary to determine theresponse of the aggregate device is not practical to implement oradvised. Thus, final determination of desired operation will generallyrequire actual measurement followed by iterative design.

In iterative design, the initial reflectarray design from modeling canbe tested with an interferometer, such as the Twyman Green. In theTwyman Green configuration, it is possible to measure the reflectedphase behavior of the initial design to incident monochromatic,collimated light, assuming some nominal conditions, by calculating therelative phase change from the shifting of the interference fringes.These measurements can be compared to modeled results and furtherrevisions can be made to improve the design, if desired.

For operation at sub-millimeter and infrared wavelengths, fine geometryfeatures are required, such as submicron line widths. One method forforming the required fine features is using electron beam lithography(EBL). Although EBL is preferred, other methods for forming finefeatures may be used with the invention including optical lithography ornano-imprint lithography.

As described below, several insights were necessary to arrive at thepresent invention that were contrary to the understandings andexpectations known by those having ordinary skill in the art at the timeof the invention. Moreover, the invention provides several unexpectedresults and at least one new application.

Regarding materials, in traditional RF designs, material dispersion isnot normally a design constraint or consideration. However, at infraredand shorter wavelengths, very few materials illustrate stable materialcharacteristics (electrical conductivity or permittivity) over theentire spectral band. Not only does this place an additional constrainton the design of a hypothetical IR reflectarray, but it gives rise toquestions regarding what type of bandwidth could be expected from such areflectarray. For example, prior to the invention it was not clear whatresponse would be produced by illuminating a hypothetical IRreflectarray at a frequency that is not the design frequency. At RF,this can be easily predicted with a good degree of accuracy using fairlysimple analysis or modeling. At IR, however, predicting this behavior isconsiderable more problematic with the variation of material propertiesdirectly impacting in a generally adverse manner reflectarray behavior.

Regarding fabrication, at RF, electrical conductivity is generally veryhigh and often is treated as perfect or nearly perfect. However, theelectrical conductivity of most metals varies significantly withfrequency. At IR, the electrical conductivity is general much lower andlossier making modeling and device design more difficult. For example,even gold, found to be one of the best electrical conductors at IR, hasan electrical conductivity about 100 times smaller than its DCelectrical conductance.

Regarding aperture size, conventional RF reflectarrays may only require100 or less elements, such as for a reflector dish system. Even known(non-integrated) millimeter wave designs utilize only a few thousandelements. Prototypes described herein have been found to require severalmillion elements for practical IR operation, such as for processingtypical laser spot sizes or collimated space, for example, 17.2 millionelements for devices described herein.

The response of the reflectarray according to the invention has beenfound to be driven by aggregate or array response more than theindividual elements making up the array. In RF systems having about 100elements, it is critical that each individual element in the designdeliver the desired phase response. Thus, in such a system, one elementcan greatly change the behavior of the reflectarray. In a reflectarraysystem with several million or billion elements according to theinvention, although a single element will give rise to some limitedvariation, it is highly unlikely that variation will give rise to anynoticeable change in the optical response of the reflectarray. Instead,the optical response will be driven by the aggregate response of all theelements in a region of size corresponding to the spatial resolution ofthe system. In turn, this leads to the realization of composite arraysaccording to the invention. One possible way to meet an arbitrary phaseresponse, is to create a periodic array of multiple elements (e.g. twodifferent elements next to each other) such that the aggregate array ofthe elements provides the desired single phase response.

Applications for reflectarrays according to the invention include planarfocusing elements, with or without polarization sensitivity. Anotherapplication includes aberration correction or characterization. Inaberration correction, the layout of the reflectarray elements arearranged introduce a phase variation upon reflection for the purpose ofcompensating phase aberrations in the incident phase front. A variety ofother related devices can be formed using the invention. Radiationdetectors can be formed by configuring the array elements to provide ahighly transmissive band adjacent to a reflective band or to providesimultaneous detection and phase front augmentation. A device cancomprise a plurality of stacked reflectarrays, where one reflectarrayacts as a ground plane for the array stacked thereon for the purpose ofbroadband or multiple band operation.

Although describes above as being either a CR or DR, dielectricelements, voids and electrically conductive elements be combined, suchas each having a portion of the area of an array. Such a design could beused for dual frequency designs with one portion of the array resonatingat one frequency and the other resonating at a different one. It mayalso be possible to stack the designs, with the DR being a low lossalternative to stacking lossy conductive layers on top of one another.

Examples

The present invention is further illustrated by the following specificexamples, which should not be construed as limiting the scope or contentof the invention in any way.

Fabrication was performed using an initial proof of concept CR design300 shown in FIG. 3( a). Each of the three (3) stripes 305 included aplurality of metal patches 310. Such a design is not a practical design.The first step involved verifying a variable-size-patch reflectarray atinfrared frequencies. An optically flat fused silica substrate having aZrO₂ dielectric (480 nm) backed by a gold ground plane with three rows(stripes) of identical-element arrays with each row made up of differentsized gold square patches (2.98, 3.14, and 3.24 μm for the first proofof concept device and 2.82, 2.90, and 3.48 μm for the second proof ofconcept device) being 150 nm thick was fabricated. FIG. 3( b) is ascanned image showing three (3) rows of elements, the rows being equallyspaced, with each row having different size elements. The unit cell sizewas held constant at 5.54 μm by 5.54. The fabrication process compriseddepositing a gold ground plane (reflective surface) on the back of theoptical flat followed by a ZrO₂ dielectric layer on the topside of theoptical flat. To adhere the gold to the optical flat and the ZrO₂dielectric layer, a 10 nm Ti seed layer was utilized. Resist was spun onto the dielectric layer followed by pattern writing using E-beamlithography. The resist was developed to expose the desired pattern andthe wafer surface was then metallized with the 10 nm Ti seed layerfollowed by gold deposition using an e-beam evaporation process. Aresist lift-off process was then used to remove excess metal and resistand reveal the metallized pattern.

Each stripe on the optical flat contained 5,000 by 1,146 elements. Theresulting SMR thus comprised 17.19 million elements. A scanned image ofthe resulting wafer is shown in FIG. 4 which has sufficient resolutionto show the individual array elements 410 within one of the stripes.

To test the prototype CR fabricated, an interferometer was utilized toverify that a different phase shift was introduced by each stripe on theoptical flat. FIGS. 5-7 are scanned images of the reflectarray taken byan interferometer operating at 28.28 THz and then smoothed in postprocessing. FIG. 5 is an interferogram of a coated flat with no patches(a control), showing no reflected phase modification. FIG. 6 is aninterferogram with fringes across the device according to the inventionillustrating variable phase modification between each stripe due to thevariable patch sizes of the device. FIG. 7 is an interferogram withfringes across the device illustrating variable phase modificationbetween each stripe due to the variable patch sizes of the device, whichis different then the first device.

This invention can be embodied in other forms without departing from thespirit or essential attributes thereof and, accordingly, referenceshould be had to the following claims rather than the foregoingspecification as indicating the scope of the invention.

1. An integrated sub-millimeter and infrared reflectarray, comprising: areflective surface; a dielectric layer disposed on said reflectivesurface, and a subwavelength element array electromagnetically coupledto said reflective surface, said subwavelength element array comprisingat least one of: (i) a plurality of electrically conductivesubwavelength elements on said dielectric layer, (ii) said dielectriclayer comprising a plurality of dielectric subwavelength elements, and(iii) said dielectric layer comprising a plurality of embeddeddielectric subwavelength elements, wherein said subwavelength elementarray in (i), (ii) and (iii) includes at least one of a plurality ofsubstantially different microscale inter-element spacings and aplurality of substantially different microscale dimensions for saidplurality of elements, wherein an operating frequency band provided bysaid reflectarray is in a range between 1 THz and 500 THz.
 2. Thereflectarray of claim 1, wherein said array comprises said (i) pluralityof electrically conductive subwavelength elements on said dielectriclayer.
 3. The reflectarray of claim 1, wherein said element arrayincludes said plurality of substantially different microscaleinter-element spacings.
 4. The reflectarray of claim 1, wherein saidplurality of embedded dielectric subwavelength elements comprise voidsin said dielectric layer.
 5. The reflectarray of claim 4, wherein saidplurality of embedded dielectric subwavelength elements comprise adielectric material having a dielectric constant lower than a dielectricconstant material comprising said dielectric layer.
 6. The reflectarrayof claim 1, wherein said array comprises ii) said dielectric layercomprising a plurality of dielectric subwavelength elements.
 7. Thereflectarray of claim 1, where said plurality of subwavelength elementshave a length and width dimensions both from 1 to 10 microns.
 8. Thereflectarray of claim 1, wherein said dielectric layer comprises ZrO₂ orBCB.
 9. The reflectarray of claim 1, wherein said subwavelength elementarray comprises said (i) plurality of electrically conductivesubwavelength elements on said dielectric layer, said (i) plurality ofelectrically conductive subwavelength elements comprising hundreds ofthousands, millions, or billions of said electrically conductivesubwavelength elements.
 10. The reflectarray of claim 1, wherein saidsubwavelength element array comprises said (ii) dielectric layercomprising a plurality of dielectric subwavelength elements, said (ii)plurality of dielectric subwavelength elements comprising hundreds ofthousands, millions, or billions of said dielectric subwavelengthelements.
 11. The reflectarray of claim 1, wherein said subwavelengthelement array comprises said (iii) dielectric layer comprising aplurality of embedded dielectric subwavelength elements, said (iii)plurality of embedded dielectric subwavelength elements comprisinghundreds of thousands, millions, or billions of said embedded dielectricsubwavelength elements.
 12. An integrated sub-millimeter and infraredreflectarray, comprising: a reflective surface; a dielectric layerdisposed on said reflective surface, and a subwavelength element arrayelectromagnetically coupled to said reflective surface, saidsubwavelength element array comprising at least one of: (i) a pluralityof electrically conductive subwavelength fixed thickness elements onsaid dielectric layer; (ii) said dielectric layer comprising a pluralityof dielectric subwavelength fixed thickness elements, and (iii) saiddielectric layer comprising a plurality of embedded dielectricsubwavelength fixed thickness elements, wherein said subwavelengthelement array in (i), (ii) and (iii) includes at least one of aplurality of substantially different microscale inter-element spacingsand a plurality of substantially different microscale dimensions forsaid plurality of element; wherein an operating frequency band providedby said reflectarray is in range 1 THz and 500 THz.